Ink jetting devices are known in the art, and thus extensive description of such devices is not required herein. As described in U.S. Pat. No. 6,547,380, incorporated herein by reference, ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field that adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
There are at least three types of drop-on-demand ink jet systems. One type of drop-on-demand system is a piezoelectric device that has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. Another type of drop-on-demand system is known as acoustic ink printing. As is known, an acoustic beam exerts a radiation pressure against objects upon which it impinges. Thus, when an acoustic beam impinges on a free surface (i.e., liquid/air interface) of a pool of liquid from beneath, the radiation pressure which it exerts against the surface of the pool may reach a sufficiently high level to release individual droplets of liquid from the pool, despite the restraining force of surface tension. Focusing the beam on or near the surface of the pool intensifies the radiation pressure it exerts for a given amount of input power. Still another type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink vehicle (usually water) in the immediate vicinity to vaporize almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands.
In inkjet printing processes and other inkjet recording processes, it is necessary that the ink being used meet various stringent performance characteristics. These performance characteristics are generally more stringent than those for liquid ink applications, such as for writing instruments (a fountain pen, felt pen, and the like).
Further, there are many requirements for the compositions including the above-described inks for inkjet recording, and specific examples thereof include. (1) no clogging of nozzles of inkjet recording heads; (2) superior ejection stability and frequency responsiveness; (3) good recovery of smooth ink ejection after residing in printhead for a long time, such as greater than two weeks; (4) no partitioning even after long-term storage; (5) no corrosion-deterioration of members, such as the recording heads, which contact therewith; (6) provision of favorable printing quality; (7) safety and no unpleasant odor; and the like.
Various inks for inkjet printing processes are known in the art. For example, various inkjet inks are disclosed in U.S. Pat. Nos. 4,737,190 and 5,156,675.
Although numerous inkjet inks are presently available, they generally do not meet all of the above-described requirements, while also providing excellent print quality on plain paper. In particular, the inks generally used in inkjet printing processes, while producing acceptable print quality, do not produce the high print quality that is achieved by using dry toner compositions, such as in electrostatographic imaging processes.
A need continues to exist in the inkjet industry for improved inkjet inks, and processes for producing the same, that satisfy the above-described requirements while providing high quality prints on a wide variety of recording media, including plain paper. Although some currently available inkjet inks may provide waterfast images with better substrate latitude, the inks are unacceptable in that they generally smear, have poor latency and maintainability characteristics, and are not easily marked on after the image is produced. Thus, there remains a need in the inkjet ink industry for improved black and colored inks that satisfy the above requirements, and allow for the printed image to be marked on after it is produced, without beading or smearing of the subsequently applied marking.
One type of inkjet ink that is commercially available is a solid inkjet ink that contains non-polar molecules as its major components. One of the major problems with current solid inkjet inks is the non-polar nature of the major ink components, which hinders the ink adhesion to the paper fibers and does not readily allow for the printed image to be marked on after it is produced. As a result, scratch resistance and fold properties as well as marking characteristics after the image is produced with current solid ink jet inks are in need of improvement.
The current solid inkjet ink preparation process uses about 5 polymeric components and requires a jetting viscosity of almost 11.2 cps that is reached at a temperature of 135° C. and a standby temperature of 110° C. Unfortunately, the current solid or phase change inkjet ink printing process can consume a lot of energy to produce an image with inadequate fold and scratch resistance properties, and undesirable marking characteristics after the image is produced.